The present invention relates to the production of sequential beams of penetrating electromagnetic radiation and, in particular, to the generation of sequential and parallel beams of radiation in the x-ray region of the electromagnetic wave spectrum.
For many applications of x-ray radiation, steerability of the x-ray illumination is advantageous. Methods currently employed for providing a beam that either scans periodically or may be directed to a specified direction are typically massive and slow. This is because current methods attempt to steer the x-ray radiation either by moving the source in its entirety, or by physically moving massive collimators interposed in the path of the x-ray beam. Mechanical scanning systems use x-ray tubes in which the electron beam trajectory is fixed. Consequently, the areas that may be scanned at a given time are limited by how fast the device which steers the x-ray beam can be moved. Further, lead is usually used to absorb any radiation that is undesirable, which makes current x-ray steering devices heavy and awkward.
Additionally, with fixed electron beam sources, x-ray imaging may be distorted. This is because the x-ray beams pass through an inspected region at different angles thereby subtending different volumes of the inspected object. Mechanical chopper systems with fixed beam size also have a fixed spatial resolution at a fixed distance from the x-ray generator so zooming, or magnification of the image of a particular region of an inspected object, can only be accomplished by manipulating the image pixels.
In accordance with one aspect of the invention, in a preferred embodiment, an apparatus for generating sequential beams of penetrating electromagnetic radiation is provided. The apparatus includes a source for producing a beam of charged particles and a target. An electromagnetic steering device directs the charged particles to strike the target at a substantially ninety degree angle. The target receives the beam of charged particles and, consequently, emits electromagnetic waves. The electromagnetic waves pass through a collimator and emerge from the array of transmitting regions in a series of parallel beams of electromagnetic radiation as the beam of charged particles is directed at a plurality of specified locations on the target.
In accordance with another aspect of the invention, an apparatus for generating penetrating electromagnetic radiation of variable beam opening is provided. The apparatus has a source for producing a beam of charged particles, a target, and at least one collimator that is moveable in a direction normal to the target in such a manner as to change the spatial resolution.
In accordance with further embodiments of the apparatus, the collimator includes apertures in an absorbing matrix. The absorbing matrix may be lead or mercury. In another embodiment, the collimator includes substantially parallel transmitting rods in an absorbing matrix.
In other preferred embodiments, the source for producing a beam of charged particles includes an electron gun or an ion beam gun. The source for producing a beam of charged particles may also be a cathode ray tube. The charged particles may also be accelerated toward the target such that they attain relativistic energy.
In accordance with another aspect of the invention, a method for generating sequential beams of penetrating radiation is provided in which a source for producing charged particles supplies a beam of particles which is directed to a plurality of specified locations on a target. The charged particles are steered such that they hit the target at a substantially ninety degree angle, and radiation is produced which is then collimated. In a preferred embodiment, the position of the collimator with respect to the source of radiation can be varied such as to change the spatial resolution of the beams and thus produce a true zooming effect.
In accordance with a further aspect of the invention, an improvement is provided to a system of the kind employing penetrating radiation for characterizing an object concealed by a concealing surface. The improvement has an apparatus for generating sequential beams of penetrating radiation. The apparatus includes a source for producing a beam of charged particles, a target, a electromagnetic steering device to force the charged particles to strike the target at a substantially ninety degree angle, and a collimator having an array of transmitting regions disposed near the target. Electromagnetic waves emitted from the target pass through the collimator and emerge from the array of transmitting regions in a series of parallel beams as the beam of charged particles is directed at a plurality of specified locations on the target. The penetrating radiation may also be multiplexed to provide a seamless image.
In accordance with yet a further aspect of the invention, an improvement is provided to a system of the kind employing penetrating radiation for characterizing an object concealed by a concealing surface. The improvement has an apparatus for generating penetrating radiation of variable beam opening. The apparatus includes a source for producing a beam of charged particles, a target, an electromagnetic beam director, and at least one collimator that is moveable in a direction normal to the target in such a manner as to change the spatial resolution.
In accordance with another preferred embodiment of the invention, a method is provided for varying spatial resolution of an imaging system wherein a source for producing charged particles and a collimator are provided, the particles are directed to a plurality of specified locations on a target to produce penetrating electromagnetic radiation, and a distance between the target and the collimator is adjusted. The electromagnetic radiation may also be multiplexed to provide a seamless image.
In accordance with another embodiment of the invention, a system is provided for inspecting the contents of containers which includes a first source for emitting a beam of penetrating electromagnetic radiation from an addressable position on a target in a first direction, a conveyor for moving the container relative to the first source, a second source for emitting penetrating radiation in a direction substantially opposite to the first direction, a first detector for detecting radiation emitted by the first source and generating a first signal, a second detector for detecting radiation emitted by the second source and generating a second signal, and a controller for characterizing the contents of the container based at least on the first and second signals.